The present invention relates to a flat article conveyor and particularly relates to a conveyor for use in conjunction with automated circuit board manufacturing equipment where conveyors typically transport circuit boards between individual workstations.
In many manufacturing processes, it is conventional to transport an article between various workstations where different types of machines perform various operations on the article undergoing manufacture. For example, in the manufacture of printed circuit boards, many specialized manufacturing operations are performed at various and different workstations. Frequently, however, the boards are transported manually between the workstations. At each workstation, an operator typically removes a board from an input tote box, loads the board into the machine's fixture, waits for the machine to perform its specialized operation on the board and then removes the board from the fixture and disposes it into an output tote box. The tote boxes are, of course, manually moved between the workstations and this sequence of operations is repeated at each of the various workstations.
Automatic conveyance of articles between workstations is, of course, not new per se. However, specialized problems occur in efforts to convey articles, for example, printed circuit boards, in the automated manufacture thereof. For example, it is desirable that the boards be movable bi-directionally and with accuracy into predetermined positions after such movement. The magnitude and direction of forces acting on the moving circuit board must be maintained within predetermined levels. Access to the top and bottom of the boards must be virtually unlimited. Also, transfer problems occur when boards are transferred from one conveyor to the next or from one workstation to a conveyor or the converse. Such problems include boards jamming in the conveyor or electrostatic charge build-up on the board and sudden electrical discharge, which may cause damage to the circuit components of the board. Modularity of system components for serviceability and flexibility, together with low complexity and cost, are also considerations which must be addressed in the provision of a flat article conveyor of the type for transporting printed circuit boards.
One example of a prior flat article conveyor for conveying printed circuit boards between manufacturing workstations is described and illustrated in U.S. Pat. No. 4,561,819, issued Dec. 31, 1985. That patent alludes to various types of conveyors, for example, belt conveyors, push/pull devices, chain conveyors, and vibration conveyors, all of which have been used in the past and have met with limited degrees of success in minimizing or eliminating the foregoing and other problems associated with the conveyance of flat articles, e.g., printed circuit boards.
According to the present invention, there is provided a flat article conveyor particularly adapted for the conveyance of printed circuit boards between various types of workstations. More particularly, the conveyor hereof includes a pair of endless conveyor belts on respective opposite sides of the conveyor, each belt being disposed about pulleys or rollers at respective opposite ends of the conveyor. Inside portions of the belts are thus spaced laterally one from the other and serve as transport mechanism for the boards. In accordance with a particular aspect of this invention, the belts are disposed on edge and for movement about pulleys having substantially vertical axes adjacent opposite ends of the conveyor. Thus, each belt has a height dimension greater than its width dimension, the width dimension being transverse to the direction of movement of the conveyor and in the plane of movement of the articles along the conveyor. The opposite lateral edges or margins of the printed circuit boards rest on the upper edges of the laterally spaced belts.
The pulleys at opposite ends of each conveyor section on opposite sides of the conveyor have laterally outwardly projecting flanges at their lower ends for engaging and guiding the lower edge of the associated belt. The upper portions of the pulleys are otherwise free of projecting flanges or guides such that the area above the upper belt edge, particularly adjacent the pulleys, is free to support a margin of the printed circuit board on the conveyor. For reasons outlined in detail hereinafter, the upper edge of each belt is beveled or inclined in an outward and downward direction away from the pulleys, the beveled upper edges of the belts underlying the circuit boards supported therebetween on the upper edges of the belt.
The belts are preferably formed of a fiberglass-reinforced conductive rubber to provide a high coefficient of friction between the conveyor belts and the conveyed circuit board. This eliminates any need for pusher-type devices or squeezing or clamping of the board while the board is moving along the conveyor. Also, with such high coefficient of friction, the board may be transported in opposite directions simply by reversing the direction of the conveyor. It will be appreciated that the high coefficient of friction between the belt and the board, together with the known acceleration/deceleration profile of the belts, also affords accurate positioning of the board after rapid movement and prevents loss of registration of board position relative to belt position. Consequently, the acceleration and deceleration forces acting on the board may be maintained within predetermined levels.
Additionally, the on-edge conveyor belts are provided with upstanding, generally U-shaped, guides which receive the inner runs of the belts between the pulleys. The upstanding legs of the U-shaped guides between the belts terminate short of the upper edges of the belts so that the printed circuit board may be transported on the belt edge. The other upstanding legs of the guides within each endless belt extend upwardly above the upper belt edges to afford lateral guides for the printed circuit boards.
By providing a belt-on-edge configuration and mounting the boards on the upper thin edge of the belts, maximum access to the upper and lower surfaces of the boards is obtained. This is significant in certain printed circuit board manufacturing operations. Additionally, the beveled upper edge of the belt facilitates transfer of boards or flat articles from one conveyor to the next conveyor. More particularly, if adjacent transfer conveyors are slightly misaligned one with the other, either elevationally or laterally, the beveled configuration facilitates the transfer of boards from the feed conveyor to the receiving conveyor. For example, while conveyors of this type are normally disposed at the same elevation, it is possible due to different tolerances for the receiving conveyor to be slightly higher than the feed conveyor. In those circumstances, the board advances from the feed conveyor into contact with the beveled edges of the receiving conveyor. Those beveled edges assist in displacing the board vertically upwardly onto the flat upper edges of the belts of the receiving conveyor. Typically, of course, there is no problem if the receiving conveyor is slightly below the elevation of the discharging conveyor. The beveled edges also facilitate in much the same manner the transfer of boards which are warped from one conveyor to the next and whether or not the conveyers are misaligned.
As a further example, if adjacent conveyors are laterally misaligned, the longitudinally adjacent pulleys of the feed and receiving conveyors have heights which extend above the upper edge of the belts. Upon slight lateral misalignment of these conveyors, the leading edge or corner of the circuit board edge on one side of the discharge conveyor will engage the portion of the pulley on the corresponding side of the receiving conveyor above the belt thereof. The rotation of the receiving pulley tends to displace the board toward the center of the conveyor and align it between the side guides of the conveyor.
A further feature of the present invention resides in the bias applied to the belts to maintain the belts in contact with the underlying guides and the flanges of the pulleys. This enables the upper edges of the belts to remain free and unobstructed to receive the margins of the printed circuit boards. To achieve this, the axes of rotation of the pulleys on each of the opposite sides of the conveyor are slightly misaligned such that they converge towards one another below the conveyor. This causes the belts to bear or track against the bottom guides and the pulley flanges. This convergence of rotational axes may be accomplished by mounting each pulley for rotation about a single bearing carried by a pulley hub and located above the longitudinal centerline of the belt. Consequently, when the belt is driven, an off-center load is placed on the bearing, causing the bearing to shift to the loaded side of its raceway. This enables the outer race of the bearing and hence the pulley to rotate about an axis angularly related to the axis of the inner bearing race which is true vertical. Consequently, the outer races and, hence, the pulleys of each conveyor section, cant toward one another to provide downwardly slightly convergent axes of rotation. Thus, the entire upper edge of each belt is free for use as a support surface for the margin of the board obviating the need for upper belt guides or pulley flanges. That is, the belts are maintained seated against their underlying guides.
Additionally, by using conductive elastomer belts, conductive polymer belt guides, metal guide rollers and support frames, continuous bleed-off of any accumulated static electrical charge is assured. Additionally, the conveyors may be provided in usable sections of predetermined length, for example, on the order of 18 to 36 inches per section. Consequently, this modular aspect provides for individual positioning of the board and individual conveyor module serviceability.
Accordingly, in accordance with a preferred embodiment of the present invention, there is provided a conveyor for transport of articles having opposite side edges, comprising a flexible endless conveyor belt disposed along one side of the conveyor and spaced laterally from the opposite side of the conveyor, the belt extending generally parallel to the direction of travel along the conveyor, a pair of rollers mounted adjacent opposite ends of the conveyor for rotation about spaced, generally vertical, axes, the belt extending about the rollers and having, in cross-section, a depth dimension greater than its width dimension for supporting articles along its upper surface, the upper surface and the side of the belt closest to the opposite side of the conveyor being beveled to provide an inwardly facing beveled surface along the longitudinal extent of the belt.
In another preferred embodiment hereof, there is provided a conveyor for transport of articles having opposite side edges, comprising a flexible endless conveyor belt disposed along one side of the conveyor and spaced laterally from the opposite side of the conveyor, the belt extending generally parallel to the direction of travel along the conveyor, a pair of rollers mounted adjacent opposite ends of the conveyor for rotation about spaced, generally vertical, axes, the belt extending about the rollers and having, in cross-section, a depth dimension greater than its width dimension for supporting articles along its upper surface, a guide surface underlying the belt, the guide surface defining an elongated groove for receiving the belt with the height of the guide surface along the inside face of the conveyor belt being less than the depth dimension of the belt.
Accordingly, it is a primary object of the present invention to provide a novel and improved flat article conveyor which affords bi-directional movement and accuracy of positioning of the article, maximizes access to the top and bottom areas of the article, facilitates transfer of the article from adjacent in-line conveyors, as well as drain of any electrostatic charge from the articles being conveyed, provides modularity of system components and minimizes complexity and cost.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification and appended claims and drawings.